Status of contents after final walk through.

You can sue them if they removed anything that contractually (as per the contract of sale or any addenda to it) that they were supposed to leave (i.e. that you were purchasing with the home) for breach of contract. You would sue for the value of whatever they took.
If they withheld keys for a time but you now have access, you can also sue for any costs you incurred due to their wrongful act of withholding the keys: e.g. locksmith costs to gain entry and rekey; storage, if you had to temporily store belongings elsewhere, because you could not move them in; etc. Again, it would be for breach of contract--they were contractually obligated to turn over the keys and possession at closing.
If still can't get in for some reason, you could bring the legal action on an "emergent" (think "urgent" or "emergency") basis to get a court order that they must give you the keys and let you in.
If you need an order for access, hire an attorney to help you: suing for court orders is generally more complex than suing just for money, and suing on an emergent basis is more complex yet. If you just want monetary compensation, then if the amount is less than the small claims limit, you probably should sue in small claims court, as your own attorney ("pro se") to save on legal fees, since you can't get them to pay for your lawyer (unless the contract of sale says that if you have to sue and win, they will pay for the attorney, etc.).